Floating rotation mandrel for finning



June 8, 1965 w FLOATING ROTATING MANDREL FOR- FINNING Filed Dec. 11. 1961 INVENTOR.

United States Patent Michigan 1 11, 1961, Ser. No. 158,264

Filed Dec.

9 Claims. (Cl. 72108) The present invention relates to an improved floating rotating mandrel for finning metal tubing, in particular tubing intended for use in heat transfer applications. The mandrel is of the general type illustrated and described in the patent to Greene and Keyes, No. 2,761,336 of September 4, 1956, in that it employs a mandrel which floats freely within a metal tube while coacting with finning discs or roller means with which the tube has relatively rotatable engagement in the operation, as distinguished from previous commonly employed mandrel rigidly supported at the rear thereof by an elongated mounting rod.

It is a general object of the invention to provide a floating mandrel which, in addition to its floating action within the tube, also has components whch freely rotate with the tube and relative to one another in the finning operation of associated finning or grooving discs... Thus, acornbination of pilot and internal forming mandrel components are rotatably supported in coaxial, end-to-end relation to one another upon an internal bearing support or rod holding the components, as well as certain interposed antifriction washers or spacers, in a unitary assembly.

Such provisions make possible a floating and rotating mandrel which accommodates, at the various component pilot and forming parts thereof, the various tube supporting and constricting and grooving, or finning, forces externally imposed on the tube surrounding the mandrel. That is, the ability of each component member of the mandrel to rotate freely prevent the building up of opposing or counteracting forces at the mandrel, and thus allows the metal to flow over the mandrel freely while keeping it in place in the axial sense within the tube and preventing the tube from tearing.

Another general object is to provide-a floating and rot-ating grooving or firming mandrel which, by reason of its composite construction as described, enable the ready production of extremely long lengths which are very straight. p i

A still further object of theinvention is to provide a mandrel of the type described composed. of successive a pilot and forming sections of tungsten carbide or like extremely hard alloy to withstand the action of the grooving discs on the tube without indenting such sections, with certain of these sections spaced for independent rotation upon an internal elongated bearing rod by annular spacers or sleeves of a suitable bearing metal, such as bronze, yet

wtih certain of such hard sections which serve as pilot and forming components of the mandrel at a zone of critical forming action being indirect end engagement with one another for independent rotation, in vie-w of the heavy axial thrust at this zone which would unduly wear a softer metal.

The foregoing as Well as other objects will become more apparent as this description proceeds, especially when considered in connection with the accompanying drawing illustrating a preferred embodiment 'of the invention, wherein: i f i FIG. 1 is a fragmentary longitudinal view showing the mandrel as operatively associated with grooving or finning discs and a metal tube, the latter being shownin axial section and the mandrel being shown as partially broken away and also in axial section; and p FIG. 2 is an end View ofthe mandrel, as from the right of FIG. 1. I t The improved mandrel of the invention is generally 3,187,537 Patented June 8, 1965 designated by the reference numeral 10; and it has at its center an elongated bearing and mounting rod 11 of a suitable composition of bronze, brass or other appropriate bearing metal.

This rod 11 is an integral one extending the entire overall length of the mandrel 10. It is comprised of a cylindrical portion 12 of substantial length and of a diameter substantially less than that of a metal base tube 13 to be finned. The rod 11 extends forward of this portion 12 in a reduced diameter at 14, upon which it rotatably sustains a number of forming and pilot mandrel sections (hereinafter described); and still further forwardly or to the right (FIG. 1) terminates in a reduced diameter threaded extremity 15, to which flat sided securing and lock nut 16, 17 are applied.

Rearwardly of the cylindrical body portion 12 of rod 11, the latter is reduced in diameter at 19, at which portion it receives a felt oiler ring or sleeve 20 whose outer diameter substantially equals the ID. of the base tube 13 being finned. The components are held in assembly at this end by jarn nuts 21 threadedly applied to the outer end of reduced rod portion 19, with a pressure washer 22 acting between these nuts and the oiler ring or sleeve 20. The latter is, of course, appropriately impregnated with lubricant to facilitate the forming and finning operation by reducing friction between tube 13 and mandrel 10.

A set of tube reducing and grooving or finning disc units coacts with the mandrel 1G in the basic manner described in the patent to Greene et al identified above. This set may comprise assemblies 24, 25 of rolling, and grooving or finning discs 26 of a known type mounted upon arbors 27, 28, respectively. Ordinarily there are three such sets spaced equally in the circumferential sense about the axis of mandrel 1t and tube 13, although this is not always the case; and provision of a known sort is made to bring the sets 24, 25 strongly inwardly radially under heavy pressure to initiate and complete the reduction of the tube 13 in diameter at 39, and to form, tin or groove the latter. This will preferably involve a progressively increased application of finning pressure to the tube by the discs 26,-in the manner illustrated and described in the patent to Hill, No. 2,508,518 of May 23, 1950.

The axes of the discs 26 are inclined at a desired angle to the tube axis so as, in conjunction with the mandrel, to conjugate with and form an extruded helical fin on the tube; and for this purpose, appropriate known means are provided to produce relative rotation of the tube and disc sets 24, 25, in reference to the axes of mandrel 10 'ice and tube 13, such that the disc sets produce an axial forward advance of tube 13 as the'forming, grooving and finning proceeds. i

As held in place upon the rod 11 between the respective pairs of end nuts 16, 17 and 20, 21, yet not under sufiicient axial force to substantially impede the independent rotation of its pilot and forming components, the mandrel 10. includes the following. i

There is a primary carbide mandrel section 32 which is sleeved upon the reduced forward portion 14 of rod 11 as a bearing, and ultimately takes its forming position, illustrated in solid line in FIG. 1, just to the rear of the finning and grooving sets 24, 25. The forming section 32 is of relatively short axial length, for minimum rotative friction on the rod 11, and its forward side is shaped to provide an annular forming or abutment shoulder 33 of relatively sharply convex curvature. The rear radial surface of the sleeve-like primary forming section 32 has running engagement against the forward end of a secondary or pilot mandrel 35, also of tungsten carbide to reportion 14 (as do other mandrel sections to be described) amounting to in the neighborhood of 0.002 inch, although I 'stantially less than the inner diameter of the base tube 13 being finned, needing a substantial radial reduction of tube diameter at the forming and finning sets 24, 25.

An anti-friction bronze washer 37 sleeved on rod por tion 14 to the rear of pilot mandrel section 35 separates the same from the forward end of the integral enlarged cylindrical portion or formation 12 of the rod 11, which thus rearwardly sustains the assemblage of pilot and formingmandrel sections against a Very substantial axialthrust at the forming or abutment shoulder 33 of mandrel section 32. It is to be noted that whenmandrel lit is inwardly inserted in the tube body 13 for the firming operation, its carbide forming and pilot sections will be spaced somewhat to the rear of the disc sets 24, 25. The action of the latter in commencing reducingand finning operation on the tube is to draw the mandrel forwardly from the dotted line position indicated in FIG. 1 t the solid line position, in which the shoulder 33 directly sustains the axial thrust exerted by the mandrel in the finning operation. t

The mandrel is completed bya pair of like, relatively elongated, rearward and forward pilot mandrels 39, 40, respectively. These are formed of a hard, wear and indentation resistant material, such as tungsten carbide, and are separated axially bya-bronze bearing washer 41, for reduced friction operation of members 39 and 40. Finally, a small size bronze thrust washer 42 is interposed at the forward end of mandrel section 40, between the latter and the nuts 16, 17.

It is desirable to provide a small length carbide forming mandrel 32 as a component separate from the equal diameter carbide pilot mandrel 35, in the interest of reducing running friction on rod portion 14 at the critical formingzone to a minimum.

Similarly, it is desirable to provide carbide pilot structure at forward mandrel sections 39, 40 which is 0011- siderably elongated in character. These mandrel sections have the same outer diameter as the inner diameter of the finned tube portion (assuming a very slight radial outward spring or" the latter after finning) and the elongated pilot construction provides a desired length or" internal tube V bearing area to result in a very straight product. The two sections 39, 40 are employed, not only to reduce radial running friction, but also in view of the fact that it is easier to obtain a pair of carbide coacting section lengths than asingle elongated mandrel section of the overall forward pilotzlength. The 'presenceof the spacing bronze washer 41 contributes 'to a desired independence ofrotation of the sections 39, itlrelative to one another, just as the washer 37 contributes in this manner at the rear. of the forming and pilot carbide sections 35.

The invention provides a mandrel inwhich extremely long lengths of tube can be expeditiously finned with a low power requirement, in so far as producing relative;

rotation of tube and forming discs is concerned, the man drel and any or all of its sections rotating freely upon the mounting and' bearing rod, thus enabling the mandrel to'withstand the various forces in axial tension and radial V compressionto whichit is subjected at various points along its length; while the mandrel is firmly held in place at the shoulder 33 and stresses tending to 'tear the tube are prevented from arising.

The drawing and the foregoing specification constitute a description of the improved floating rotating mandrel for firming in such full, clear, concise and exact terms as toenable any'person skilled in the art to practice the invention, the'scope of which is indicated by the appended claims. I

' What I claim as my invention is: r a 1. A floating mandrel for-forming base tubing for unsupported action within the tubing, comprising a plurality of axially arranged, cylindrical mandrel sections rotatable coaxially relative to one another, including a pilot secdisposed to the rear of said pilot section, and means rearwardly sustaining said sections and mounting the same as a unit for coaxial rotation relative to one another.

2. A floating mandrel for forming base tubing for unsupported action within the tubing, comprisinga plurality of axially arranged, cylindrical mandrel sections rotatable coaxially relative to one another, including a pilot section and a cylindrical forming section of greater outer diameter than said pilot section, said forming section being disposed to the rear of said pilot section and having a convex rounded shoulder directly to the rear of the latter, and means rearwardly sustaining said sections and mounting the same as a unit for coaxial rotation relative to one another.

3. A floating mandrel for forming base tubing for unsupported action within the tubing, comprising a plurality of axially arranged, cylindrical sleeve-like mandrel sections rotatable coaxially relative to one another, includingta pilot section and a cylindrical forming section of greater outer diameter than said pilot section, said form ,in section being disposed to the rear' of said pilot section and having a convex rounded shoulder directly to the rear of the lattenand means rearwardly sustaining said sections and mounting thesame as a unit for coaxial rotation relative to one another, comprising a rod extending through said-section's, said sections having running bearing engagement on said rod.

4. A floating mandrel for forming base tubing for unsupported action within the tubing, comprising a plurality of axially arranged, cylindrical mandrel sections rotatable coaxially relative to one another, including a forward pilot section, and a pair of axially sequential cylindrical forming and pilot sections of like outer diameter and greater outer diameter than said pilot section, said last named forming'and pilot sections being disposed coaxially to the rear of said first named pilot section, and means to the rear of said last named forming and pilot sections rearwardly sustaining the latter and said first named pilot section and mounting all of said mandrel sections as a unit for coaxial rotation relative to said means and one another. i

I 5. A floating mandrel for forming base tubing for unsupported action within the tubing, comprising a plurality -cal forming and pilot sections of greater outer diameter than said pilot sections, saidlast named forming and pilot sections being disposed coaxially to the rear of said first named pilot sections, and means to the rear of said last named forming and pilot sections rearwardly sustaining the latter and said first named pilot sections and a mounting all of said'mandrel sections as a unit for coaxial rotation relative to said means and one another.

I 6. A floating mandrel for use in reducing and finning I metal base tubes by unsupported action within the tube,

comprising acylindr'ical, relatively forward pilot mandre'l section oftan outer diameter substantially equal to the desired internal diameter of a finned portion of 'the tube, a cylindrical forming mandrel section of'an outer diameter substantially greater than said pilot 'section in a forward annular shoulder zone of the forming mandrel coaxiallyrto the rear of saidpilot mandrel section, but less than the inner dia'meterof the'base tube to be finned, said sections being coaxially rotatable relative to one another adjacent said shoulder zone, said formingmandrel section having an annular shoulder at a zone which is rounded at said zone to support said tube rearwardly of said finned portion of thelatter, and means rearwardly section of an outer diameter substantially greater than said pilot section in a forward annular shoulder zone of the forming mandrel coaxially to the rear of said pilot mandrel section, but less than the inner diameter of the base tube to be finned, said sections being coaxially rotatable relative to one another adjacent said shoulder zone, said forming mandrel section having an annular shoulder at a zone which is convexly rounded radially inwardly in a relatively abrupt curvature at said zone to support said tube rearwardly of said finned portion of the latter, and means rearwardly sustaining said sections as a unit and rotatively mounting the same for said relative rotation thereof, and rotary finning disc means in rotative, radial compressive engagement with said base ,tube surrounding said mandrel, said disc means acting rotatively relative to and on said tube on a portion thereof directly forwardly of the shoulder of said forming mandrel section.

8. In combination, a floating mandrel for use in reducing and finning metal base tubes by unsupported action within the tube, comprising a cylindrical tubular, relatively forward pilot mandrel section of hard, indentation-resistant material of an outer diameter substantially equal to the desired internal diameter of a'finned portion of the tube, a cylindrical tubular forming mandrel section of similarly hard material and of an outer diameter substantially greater than said pilot section in a forward annular shoulder zone of the forming mandrel coaxially to the rear of said pilot mandrel section, but less than the inner diameter of the base tube to be finned,

6 said sections being coaxially rotatable relative to one another adjacent said shoulder zone, said forming mandrel section having an annular shoulder at a zone which is radially inwardly and convexly rounded in a relatively abrupt curvature at said zone to support said tube rearwardly of said finned portion of the latter, and means rearwardly sustaining said sections as a unit and mounting the same for said relative rotation thereof, comprising an elongated rod extending through said mandrel sections and journaling the same for rotation, said rod having means in the form of an integral formation thereon which is in rearward axial supporting relation to said sections, and rotary finning disc means in rotative, radial compressive engagement with said base tube surrounding said mandrel, said disc means acting rotatively relative to and on said tube on a portion thereof directly forwardly of the shoulder of said forming mandrel section.

9. A floating mandrel for forming base tubing for unsupported action within the tubing, comprising a plurality of axially arranged, cylindrical mandrel sections rotatable coaxially relative to one another, including a pilot section and a cylindrical forming section of greater outer diameter than said pilot section, said forming section being disposed to the rear of said pilot section and having a convex rounded shoulder directly to the rear of the latter, which shoulder extends radially inwardly of said forming section and is of relatively abrupt curvature.

References Cited by the Examiner UNITED STATES PATENTS 2,359,339 10/44 Wadell 78-103 2,668,461 2/54 Henderson 78-103 2,680,975: 6/54 Goldsmith 80-13 2,761,336 9/56 Greene et a1. 80-13 WILLIAM J. STEPHENSON, Primary Examiner. LEON PEAR, Examiner. 

1. A FLOATING MANDREL FOR FORMING BASE TUBING FOR UNSUPPORTED ACTION WITHIN THE TUBING, COMPRISING A PLURALITY OF AXIALLY ARRANGED, CYLINDRICAL MANDREL SECTIONS ROTATABLE COAXIALLY RELATIVE TO ONE ANOTHER, INCLUDING A PILOT SECTION AND A CYLINDRICAL FORMING SECTION OF GREATER OUTER DIAMETER THAN SAID PILOT SECTION, SAID FORMING SECTION BEING DISPOSED TO THE REAR OF SAID PILOT SECTION, AND MEANS REARWARDLY SUSTAINING SAID SECTIONS AND MOUNTING THE SAME AS A UNIT FOR COAXIAL ROTATION RELATIVE TO ONE ANOTHER. 